1. Field Of The Invention
The present invention relates to an environmental condition simulator for teaching pilots how to land and take-off aircraft under adverse weather conditions. More specifically, the present invention relates to an environmental condition simulator for accurately and realistically generating fog and rain conditions which will be observed by a pilot during takeoff and landing of an aircraft.
2. Description Of The Prior Art
All aircraft require some form of runway to perform either a landing or takeoff phase maneuver. Usually these maneuvers are monitored by strict Federal Aviation Administration (FAA) policies and procedures which govern the use of both the airspace and the airport runway facilities. The operation of aircraft, which are allowed to fly through an approved airspace and which are granted certain landing privileges, are monitored by the FAA by means of a flight plan. The major factors which cause both the pilot and FAA to modify this flight plan are primarily meteorological conditions. These conditions may be local and hence prevent both takeoff and landings, or they may occur enroute forcing the pilot to attempt to land at an approved alternate runway.
During the time since commercial aviation has scheduled flights for both passengers and freight, the major factor which has influenced operational costs of the above services, has been the environmental meteorological conditions. This factor also has the greatest influence in the struggle for the aircraft, passengers and freight to arrive safely at the appointed destination. Since man has been virtually unable to alter the weather, his best attempt has been to devise instruments such as an autopilot or an autoland system which could enable a pilot to safely land his aircraft successfully in spite of the adverse weather conditions. However, it has been recognized that certain climatic conditions may be unfavorable to predict a safe landing as now determined by a classification of the airport conditions. Currently, the FAA monitors the visibility conditions during periods of rain, fog, or snow, and classifies the poorer visibility conditions as Category I, Category II, Category III (a, b, or c). Respectively, Category I allows the aircraft to descend to 200 feet altitude with a measured runway visual range (RVR) of 2600 feet; Category II--100 feet altitude decision height and a RVR of 1200 feet; Category III (a,b,c) are blind landing conditions with visibility sufficient only for taxiing along the surface of the runway.
Today, in spite of all the advanced weather radar devices onboard the aircraft, cockpit instrumentation, and ground aids such as Visual Approach Slope Indicators (VASI), as well as improved approach lighting systems for low visibility final approaches, the critical problem remains that poor visibility is a major contributing factor toward most of the terminal landing approach accidents. It is therefore clear that there is a great need for reduced visibility conditions of sufficient realism to induce pilot apprehensions and reactions just before touchdown.
The aircraft industry, both civilian and military, is attempting to train their pilots through the use of simulators with visual flight attachments. Their training goal has been to reduce the overall operational aircraft flight costs. However, what has been neglected in most cases is the need to establish an adequate low visibility training program, which would allow the pilots to make better decisions in regard to the various categories of visibilities which they may encounter along the final approach path. It has been well recognized that the most crucial area of the final approach has been from the last 1000 feet altitude and 3-4 mile range. Providing that the visibility is good, the pilot usually will fly the remainder of the flight viewing the runway through the windscreen after passing through the appropriate decision height. During the pilot's normal descent he may encounter various adverse weather conditions such as fog, patchy fog, rain, or rain down-burst cells, all of which cause intermittent and extremely dangerous obscuration of the runway. Presently, there have not been any simulation devices which would adequately and realistically represent all of the above environmental conditions.
The current and most widely used technique for generating low visibility scenes for piloted operations now in use extensively throughout the world has been the utilization of an electronic fog generator device. This system operates basically from the modification of red, green, and blue video signals which originate from a color television camera and terminate at the color monitor. Several extraneous signals, pitch, roll and range are sent to the fog generator so as to provide synchronization and correct alignment of a fog video overlay with the horizon and ground view presented on the monitor. The resulting scene as viewed by the pilot through his windscreen is that of a semi-transparent shade drawn over the original television runway terrain model scene. The characteristic simulated fog reproduced in this manner is homogeneous over the primary television display scene.
Another technique for producing poor visibility in aircraft simulators was performed with an optical wedge which disturbed the light sensed by the television camera sensors. This approach was used by General Precision Systems (now Redifon) who inserted a servo controlled optical wedge in the light path of the optical probe. By raising or lowering this optical wedge the light transmission and hence the video output of the television camera was changed. The effect as viewed by the pilot was a scene of reduced brightness and contrast supposedly representative of a homogeneous reduced visibility.
The University of California at Berkeley, under the sponsorship of the FAA, constructed a large building (circa 1966) in which fog particulate was produced for the study of airport lighting systems. A 1/10th scale lighted runway was constructed and enclosed in a building approximately 1000 feet long. An overhead cable was raised about 25 feet above the ground and an aircraft mock-up was attached to this cable. Fog spray was injected into this building, the cab was then released to travel about 3 miles per hour down the suspended cable, and the observers in the cab descended thru the fog toward the 1/10th scale lighted runway. This facility did not provide any capability for providing the pilot with aircraft controls or instruments other than the one open loop cable over which the suspended cab traveled. To set up the visibility conditions for the various Category I, II, or III situations with the different lighting arrangements, the fog nozzles were activated until readings taken from a transmissometer indicated the appropriate scaled readings. At this time the fog nozzles were manually turned off and the fog remained suspended until it naturally dissipated some twenty to forty minutes later.
U.S. Pat. No. 3,436,840 to Noxon discloses another known fog simulator for training pilots. In the system of Noxon the fog is optically simulated with a wedge lamp, wedge filter and minor lamps to maintain known ratios of image brightness to fog densities. However, there is no actual generation of fog or rain in the system of Noxon.
Another electronic fog generator system is described in U.S. Pat. No. 3,524,019 to Coen. Coen discloses a fog simulator in a visual display system in which television is used to generate images. The device introduces fog effect which takes into account direction of the apparent line of sight of the aircraft. The Coen patent does not disclose the use of natural fog and/or rain chambers.
U.S. Pat. No. 3,548,515 to Simon discloses an optical day and night fog simulator for use in aircraft. The fog simulator causes an outside image to be brought into the system through telescopic optics which passes through a photographic film having a variable density to a diffuser to form a real image thereon, together with a halo of light about the image. A collimated lens system transforms the real image, together with the halo of light into a collimated beam which the pilot may view by means of a front surface mirror as a nightime or daytime fog simulation. The Simon patent does not disclose the use of natural fog and/or rain chambers.
Other prior art systems are known which are of general interest with respect to some of the separate components of the system of the present invention.
For example, U.S. Pat. No. 3,620,592 to Freeman discloses an attachment for flight simulators for producing a head-up display.
U.S. Pat. No. 2,703,488 to Gevantiman et al discloses a fog mist chamber for performing environmental tests other than in flight simulators.
U.S. Pat. No. 3,327,536 to Fitzgerald discloses an environmental testing chamber for accelerated weather conditions including a water spray. The Fitzgerald patent does not disclose the use of the test chamber in combination with a flight simulator.
All of the fog/rain simulators for aircraft teaching devices mentioned heretofore suffer from the following disadvantages.
Electronic fog generator systems when presented with raster television displays produce a homogeneous type raster fog that is not representative of any actual known fog conditions. Natural fog contains sections which are more dense than others and may move in slightly different directions with respect to each other.
Electronic fog systems cannot produce the correct fog physics such as a halo effect around a light, nor reproduce the correct absorption or scattering properties. Furthermore, color spectrum shifts due to the presence of actual fog or rain cannot be reproduced with electronic fog.
Electronic fog systems cannot produce the effect of rain upon the windscreen nor the distortions of the outside visual scene as perceived by the pilot.
Electronic fog systems cannot produce a veiling luminance effect which is present under natural daylight conditions. This veiling effect makes the fog appear more dense when illuminated with ambient sunlight.
Electronic fog systems are presented at optical infinity or in the same image planes as the landing display scene. Hence, the pilot will visually accommodate his eyes at infinity or exactly opposite the accommodation reflex that occurs with natural fog, whereby the pilot will accommodate to the windscreen area and then shift to the far field when the scene can be perceived.
Electronic fog systems cannot produce a night-time fog scene such as would occur with real fog. Real fog at night has an RVR which is about twice that for day RVR. Thus, colored lights at night may be seen at about twice the distance than that for the same day RVR. Furthermore, the light intensities at night of the runway, approach path, and surrounding airport area in the presence of low fog or rain visibility factors cannot be reproduced electronically. Color shifts and halo effects as well as other distortions due to the presence of rain or rain and fog combined cannot be done electronically.
Electronic fog systems cannot produce the effect of an aircraft passing through non-homogeneous rain cells for either day or night flight operations.
Electronic fog systems are made to alter the normal red, green, and blue video signals in order to produce a simulated low visibility condition. However, most aircraft utilize a windshield wiper blade to remove fog condensate or rain drops from the aircraft windscreen. The wiper blade performs the task of momentarily removing the film of water and thus the pilot may see an undistorted scene for a fraction of a second. Other classes of aircraft utilize air blown systems to remove water from the windscreen. In both cases with either a wiper blade or a wind blown system, distortions or aberrations are present on the windscreen which cannot be reproduced electronically.
Optical wedges located within the optical probe of terrain model television systems produce the same disadvantages as described above with respect to the electronic fog systems.
Television terrain model systems characteristically utilize a raster which is converted to a video signal as the raster sweeps from the top left to the bottom right of the camera tube and display monitor. Raster driven displays, either computer or television generated, control the movement of an electron beam and its brightness by means of signals sent to the respective horizontal and vertical deflection coils, and the video amplifier. The problem which exists for low visibility simulations with these types of raster displays, is that the monitor is made to make the scene uniformly bright from top to bottom. Since aircraft simulators with visual flight attachments present a horizon within the display scene, it would be realistically appropriate to make each individual object and hence its brightness from the horizon to the bottom of the display obey the laws of physics for which the brightness will be increased toward the bottom of the monitor by the ratio of one over the distance squared from the pilot to the object. When this factor is taken into account, the scene would be in more agreement with what would normally be perceived by the pilot whereby the bottom of the display would appear brighter and elements close to the horizon would appear dimmer in low visibility operations. Currently no compensation for this fall off in scene brightness has been corrected for, especially when used in conjunction with electronic fog systems.
The Berkeley Fog Chamber, discussed hereinbefore, produced fog in a narrow and long building. Inside this building was a 1/10 scale model lighted runway with approach lights. An unconventional cab was suspended by an overhead cable and allowed to descend down this cable toward the scaled runway at about 2-5 miles per hour. This facility did not have the following: (1) control of the fog to raise or lower the visibilities rapidly (1-2 sec or less) for various types of breakout; (2) ability to rapidly change fog density as would be encountered when actually flying thru clouds; (3) the cab was constrained to only one degree of freedom motion along the scaled runway centerline, and no other motions were present; (4) no other preprogrammed trajectory could be flown; (5) there was no provision for piloted closed loop control required for automatic landings subject to manual takeover decisions by the pilot; (6) no provision for cabin intruments; (7) approach speed toward the scaled runway was very unrealistic; (8) the pilot's eye correct height above the ground after touchdown was not accounted for correctly which would normally present different final approach and taxiing problems for large commercial aircraft.